We had a close look at the FilaFab, a "Desktop Filament Fabricator". It's pretty simple in concept: put in some plastic bits and usable 3D printer filament comes out the nozzle.
But there's a lot more to it than that. The device has been carefully designed to ensure consistent melting temperature and flow rate to produce filament with reliable diameter and appropriate characteristics.
You'll need a source of plastic that's broken down into small bits for deposition in the hopper on the top of the machine. You can obtain bulk plastic pellets at a far lower price than filament, perhaps as much as five times or more less. By the way, FilaFab handles both PLA and ABS plastic. We suspect that they could also handle other plastics with a bit of testing.
Alternatively, you could somehow break up your existing models and failed prints into small enough pieces that would fit into the hopper. FilaFab might work on a "chopper" feature in the future, but for now you'd best get out a big hammer. We think this is pretty important, because, well, we happen to have a great many failed prints in a rather large pile at our lab. And so do you.
One feature we'd like to see on the FilaFab is a spooling mechanism to capture the new filament. Hot, soft filament would wrap very neatly around an empty spool, but not so much after it cools down. Perhaps FilaFab will add a spooler to future models.
The FilaFab is now on sale for £699 (USD$1100), but we understand they are still seeking certification for sales in the USA.